The present invention relates to a gas turbine engine cooling structure that provides a cooling air flow to turbine blades, and more particularly to an Angled On-Board Injector (AOBI) that locates a metering throat at an inward angle relative to an engine centerline.
In gas turbine engines, fuel is burned within a combustion chamber to produce hot gases of combustion. The hot gases are expanded within a turbine section to produce a gas stream across alternating rows of stationary turbine stator vanes and rotating turbine rotor blades to produce power. Turbine blades and vanes are cooled by air compressed upstream within the engine and flowed to the turbine section through a secondary flow system.
Secondary flow systems transfer cooling air which bypasses the combustor from stationary cavities within the engine stator to a turbine rotor assembly for subsequent distribution to the interior of the rotor blades. For this purpose, the tangential on-board injector (TOBI) is a conventional and effective device. In particular, an inlet of the TOBI nozzle receives compressed air from the compressor to pass the cooling air through annually spaced passages that impart a swirling motion to direct the stream of cooling air tangentially to the rotating turbine assembly.
The volume and direction of the cooling air are features of the secondary flow system effectiveness and overall engine performance. The secondary flow system should provide a desired metered amount of cooling air as additional cooling air may penalize efficiency of combustion while too little cooling air may result in overheating of the turbine blades and seals.
Engine performance for a relatively small gas turbine engine may often be interrelated to secondary flow system effectiveness. Packaging of a secondary flow system may be particularly complicated, as conventional Tangential On-Board Injectors (TOBI) or Radial On-Board Injectors (ROBI) require a radial height and seal structure that may be incompatible with such relatively small packaging requirements.
Accordingly, it is desirable to provide a compact injector cooling structure for a relatively small gas turbine engine which transfers cooling air from stationary cavities within a turbine stator assembly to a turbine rotor assembly thereof, yet minimizes the required radial height and lowers losses therefrom.